The invention refers to a method for measuring mass material""s weight especially refers to the use of nuclear radiation high precision measuring of mass material""s weight with high precision nucleonic weigher (nucleon scale) to apply this method.
Nucleonic weigher (nucleon scale) is manufactured on the research basis of material""s absorption principle to gamma ray.
The existing nucleon scale""s operation principle is shown in FIG. 1. In this diagram, the nucleon scale includes a gamma radiation source (1), a gamma ray detector (2), a gamma ray radiation area (3), a speed measuring device (4), a Data Processing Unit (DPU) (5), a scale frame and protecting case (6), a conveyer belt and mass meterial (7). On the top of nucleon scale""s frame there sets the gamma radiation source and underneath the frame there sets gamma ray detector. Conveyer belt with bulk mass material go through the frame. Gamma ray radiation source steadily emits gamma ray with constant intensity. When the belt carries no material the gamma ray received by the gamma ray detector is also a constant and at same time the gamma ray detector""s output voltage is U0 and when the belt carries material a part of gamma ray emitted by the radiation source is absorbed by mass material and the rest part penetrating mass material is received by the gamma ray detector and at same time the gamma ray detector""s output voltage is Ui. According to material""s absorption law to gamma ray it is known that U0, Ui and the mass material have the following relations:
Ui=U0exe2x88x92xcexcxcfx81xcfx81dxe2x80x83xe2x80x83(1)
where xcexcxcfx81xe2x80x94material""s mass absorption coefficient to gamma ray
xcfx81xe2x80x94material""s density
dxe2x80x94material""s thickness
to move line and also to multiply S/S on the exponent so we get                                           U            i                                U            0                          =                  ⅇ                                    -                              μ                ρ                                      ⁢                          ρdS              /              S                                                          (        2        )                                W        =                  ρ          ⁢                      xe2x80x83                    ⁢          ds                                    xe2x80x83                                                      U            i                                U            0                          =                  ⅇ                                    -                              μ                ρ                                      ⁢                          W              /              S                                                          xe2x80x83            
where Sxe2x80x94material""s area on the belt to apply logarithm on both sides of formula (2) and let W/S=F, K=xe2x88x921/xcexcxcfx81 so we get                     F        =                  K          xc3x97          Ln          ⁢                                    U              i                                      U              0                                                          (        3        )            
where Fxe2x80x94material""s load;
Kxe2x80x94material""s rating coefficient;
The conveyer belt""s speed V can be measured by the speed sensor so material flow P on the belt is: P=FV
The accumulative mass material Wh moved in a period of time is:                               W          h                =                              ∑                          i              =              1                        n                    ⁢                                    F              i                        ⁢                          V              i                                                          (        4        )            
The existing scale takes K as a constant in formula (3) but actually K is not a constant and it varies with the change of belt load. The main cause is the existing nucleon scale makes 2 approximations while applying absorption law to gamma ray by material and they are:
1) to assume scattering factor=1 is to ignore the gamma ray scattering influence. In fact, the more density and thickness as mass material has, the bigger influence as scattering gets.
2) the absorption law of gamma ray by mass material requires gamma ray in parallel, but actually the existing nucleon scale is to use spot source which produces fan beamed gamma ray as shown in FIG. 2. When material is on position A the absorbed gamma ray situates on plane a-b and when material is on position B the absorbed gamma ray situates on plane c-d. Obviously c-d is greater than a-b.
Therefore, change of material load, piling shape with difference of positions plus the influence of scattering factor is the main cause to restrict measuring precision of the existing nucleon scale.
At present nucleon scales available at home and abroad all adopt mass material total weight to rate coefficient K, such as Chinese Patent ZL95106808.3 (Announced Patent No.CN1039160C). Using this method to rate coefficient K the nucleon scale records only material""s weight but not the change of material""s load so the rated coefficient K is of no relation with belt""s material load and does not meet the actual situation. Evidently the existing nucleon scale can not proceed instantaneous correction to coefficient K according to belt load variation so it has rather big measuring error with less precision.
An aim of this invention is to solve the above mentioned problem. It provides a dynamic high precision measuring method to reduce and eliminate influence to measuring accuracy in respect of change of material load, piling shape with difference of positions plus the influence of scattering factor and also to proceed dynamic correction. The high precision nucleon scale is manufactured to apply this method. In order to realize above mentioned aim the invention adopts following technique schemes:
A method for measuring mass material""s weight with high precision is to include following steps:
(1) installing multiple gamma radiation sources with corresponding gamma ray detectors and in between them to install the mass material conveyer device;
(2) measuring the gamma ray detector""s output voltages U0 with no material and Ui with material to input to DPU which is connected to gamma ray detector;
(3) using the speed sensor to measure moving speed Vi of the conveyer device to input to DPU (PLC or industrial control machine) which is connected to speed sensor;
(4) the DPU calculates the accumulative weight W transmitted in a period of time according to formula:   W  =            ∑              i        =        1            n        ⁢                  KLn        ⁢                  (                                    U              i                        /                          U              0                                )                    ⁢              V        i            
The material rated coefficient K in the formula is dynamically corrected to follow the change of mass material""s load and influence of gamma ray scattering. The above mentioned material rated coefficient K to follow the change of material load is determined by object""s rated method with following steps:
(1) to use a standard scale to read out material""s weight WaB. The conveyer device steadily transmits mass material""s load to nucleon scale for measurement;
(2) from instantaneously collected parameters of gamma ray detector""s output voltage Ui, speed sensor""s moving speed Vi, and transmission time ti to calculate formulae:       F    Ba    =                              W          B                                      ∑                          i              =              1                        n                    ⁢                                    V              i                        ⁢                          t              i                                          ⁢              xe2x80x83            ⁢                        (                      L            ⁢                          xe2x80x83                        ⁢            n            ⁢                                          u                i                                            u                0                                              )                aAVG              =                            ∑                      i            =            1                    n                ⁢                  L          ⁢                      xe2x80x83                    ⁢          n          ⁢                                    U              i                                      U              0                                          n      
Set up a coordinate system with FB as ordinate and LnUi/U0 as abscissa. According to the calculated FBa and (LnUi/U0)aAvG to determine point a in the coordinate system to get K which is the sloping rate of 0a;
(3) Corresponding to different material weights WbB, WeB, WdB . . . to adopt same method as above we can determine points b, c, d . . . in the coordinate system. Hence we get Kb, Kc, Kd . . . and functional relation of FB=f(LnUi/U0) as shown in FIG. 3.
Using multi-section""s linear relation of F=bj+kjLn(Ui/U0) to replace function FB=f(LnUi/U0) where j is linear section numbers we have following steps:
(1) to connect 0a, ab, bc, cd . . . to get each linear section;
(2) to utilize 0, a, b, c, d . . . each point""s coords value to separately get each linear section""s b and k ; or to use multi-items method to joint FB=f(LnUI/U0). For a, b, c, d . . . each point coordinates to use minimum 2 multiplication method to get coefficients a0, a1, a2 . . . aK from multi-items formula: F=a0+a1(LnUi/U0)+a2(LnUi/U0)2+ . . . +ak(LnUi/U0)k where k=0, 1, 2, 3 . . . k.
It is another object of this invention to provide a nucleon scale with high measuring precision, wide application ,good stability, small maintenance and low cost.
A nucleon scale applying above mentioned method is to include:
1-N gamma radiation sources where N=2-10.
Gamma ray detector corresponds to gamma radiation source which transfers gamma ray intensity into voltage parameter. The mass material""s conveyer device is installed between the detectors and radiation sources.
Speed sensor can measure moving speed of the mass material""s conveyer device.
Micro-computer or DPU (PLC) connected to gamma ray detector and speed sensor can calculate mass material""s accurate weight according to said method.
The forenamed gamma radiation sources can be selected from 137CS, 6Co, 241Am according to the mass material to be measured. The number of sources is determined by width of mass material""s conveyer device with optimum 2-7.
The forenamed gamma radiation sources and gamma ray detectors can be fixed on counter positions in a completely enclosed scale frame.
When using multi-section""s linear relation to joint function FB=f(LnUi/U0) the above mentioned nucleon scale is to operate according to broken line position""s process prediction scheme as shown in FIG. 4.
This invention covers following advantages:
The dynamic high precision measuring method eliminates the influence to measuring accuracy from change of mass material""s load, piling shape with difference of material positions plus the influence of gamma ray scattering factor therefore, it greatly improves measuring precision. The nucleon scale applying this method has high measuring precision to suit for wide range of material""s flow with broad field of application covering good stability and wider range of application of radiation source therefore, it is either cost effective or highly accurate, safe and reliable.